A while ago I tested the BMS 4599HE midrange compression driver which did well with the exception of IMD distortion. That blog post can be found here. After publishing the results I received information from my customer that sent me the driver that he suspects the driver may have been damaged from misuse. He promptly ordered a new driver from BMS and had it shipped directly to me for retesting. These drivers are made to order, so lead time is two months after ordering. Below are pictures of the new driver after unboxing.
Test Setup
The measurement was done with my precision AKO Pacific 7052PH which I will be featuring in another blog post. The mic is connected to my Focusrite Scarlett Solo preamp. The source is the Hypex FA501 supplied by the Topping D10S which is connected to my laptop running ARTA measurement software. I inserted a -15dB fixed resistor L-Pad to eliminate amplifier noise at idle, since I did hear some hiss with my ear up to the horn mouth.
All of the equipment is relatively affordable with the exception of the measurement microphone which costs $1,654 CAD dollars.
Test Results
The frequency response looks flatter on the new driver.
The old driver with new (red) is shown below.
Here are the other results for reference. (new driver)
Harmonic Distortion
I started with harmonic distortion measuring at 95dB test signal.
Showing the same results however with the vertical scale changed from percent to dB is shown below.
How does this compare against the old driver? Below is the same test with the old driver.
Showing the same results however with the vertical scale changed from percent to dB is shown below.
Conclusions on Harmonic
The new driver exceeds the old driver's performance on H3 and H4 by a wide margin. The new driver has H3 and H4 at -91.93dB, an astonishingly low number by any standard, even amplifiers! We see the old driver at -70.05dB which is still extremely good.
Intermodulation Distortion
This is where the old driver fell apart, providing only -50dB IMD at 95dB (4kHz). Is the new driver improved? As you can see below the new driver is marginally better at -55dB (4kHz).
For reference below is the results of the old driver under the same conditions.
Looking at the new driver however, if we lower the test SPL to 85dB we see distortion improve to -65dB. Worth noting as well, midrange performance is -80dB (500Hz) which is excellent.
-65dB performance is my own self created target for home Hifi. So in this regard the 4599HE barely gets a passing score. To highlight this I've tested the SB Audience 65CDN-T in the same test setup to see how it does. Distortion is -72dB at 85dB (4kHz).
At 95dB test signal we see distortion at -60dB (4kHz) as shown below.
Conclusion
The BMS 4599HE originally interested me because of the high sensitivity (115dB) and dual midrange diaphragm technology. I've obtained excellent results with all of the other BMS compression drivers I've tested and so I had hoped that this one would excel even further due to it's unique dual diaphragm design. The 4599HE's performance in the context of home HiFi falls slightly short of my desired target for sound quality. Although admittedly I've set the bar extremely high. I'm sure it is extremely competitive in a pro-sound application which it is originally designed for.